Variable vane turbo for 944
 

I have been meaning to post on this for months but kept forgetting. Somebody figure out how to adapt a variable vane turbo like the one in the new 997TT for our 951s. It would improve low end immeasurably and eliminate the wastegate and attendant vacuum tubing. Lindsey Racing and Russell need to get working on this immediately. I will buy one.

BTW - sorry if this has already been discussed and I missed it.

One would probably cost twice what a 951 is worth.

Maybe. But it would be interesting to find out what it would cost and if it is doable. There is an oem that makes these turbos, probably for a few applications. There are a lot of people out there with $7,000 951s with $15,000 in trick parts - (alas not mine but the total in column 2 is growing) this would be the trickiest yet.

last time i checked the 951 and its associated engine parts were made out of various types of metal. since there are no alien or abnormal use of carbon fiber :) anything is possible

It look slike its a suto internaly gated turbo (ricers usually turn away from these things because of high rpm (high air flow) boost creep.

Re: Variable vane turbo for 944
 

it's already available. why don't you get one and let us know how it works out?
http://www.turbos.bwauto.com/products/vtg.aspx

Sorry resurrect a seriously old thread but the problem with the turbos available from Borg Warner (aside from those on the 997) is stated clearly on their site:

"BorgWarner Turbo Systems currently offers various sizes of turbochargers with variable turbine geometries for diesel engines in automobiles and light commercial vehicles."

Though BW has created a great turbo for gasoline engines on the 997 the problem still remains that none of the turbos they offer would be correctly sized for application on a 944/951/968. However the BW variable turbos are still no more than a conventional turbo with a variable turbine housing. Though there is a noticeable performance difference (I have had the luxury of driving one after another, both cars with similar modifications) turbo lag is still an issue. This is due to the fact that the bearing design still remains the same as any other conventional turbo: bearing cavity in the center, flooded bearings, hot engine oil. All of which add up to friction, drag, reliability issues, and turbo lag still being an issue. Friction from heat prevents the shaft/wheels from spinning up as fast as they could. Flooded bearings means more drag, again preventing the wheels from spinning as fast as they could, causing turbo lag. Hot lubrication from the engine means that when you run your car hard you absolutely need to let it idle for a minute or two before shutting your car off the prevent the bearings and seals from cooking within the turbo.

That said I'd like to point out that a variable-vane turbo that is free from the aforementioned burdens has been in production for quite some time: the Aerocharger.
We use these turbos on an extremely wide range of applications: automotive, small engines (snowmobiles, motorcycles, ATVs, etc.), aircraft, even military applications. The technology has been proven time and time again to truly eliminate turbo lag.

The ingredients are simple: The bearing assembly is placed in front of the compressor housing, at the coldest location on the turbo where air is constantly drawn past it. Lubrication is self-contained. A small oil cavity on the front of the compressor housing provides oil to the ceramic ball bearings via wicks which mist the oil onto the bearings. This is absolutely the lowest drag lubrication system of any turbo, allowing for the fastest spool-ups in the industry. This significantly controls heat within the turbo by less friction and no engine to heat the oil. Heat transfer is controlled by a specially designed heat shield within the turbo, separating the two housings effectively. Radiant heat is controlled by a form fitting turbine heat shield for the exterior of the turbo. Several layers of header wrap can be sandwiched between the heat shield and the turbine housing to further reduce radiant heat.

Again I apologize for bring back an old thread but it's unfortunate to see people needing our turbo but don't know that it exists. Anyone can see that the 951s don't exactly have the most efficient turbo system. However to adapt on of our turbos to these cars would not only provide an excuse to redesign the exhaust side, but the turbo itself would be a night and day difference. Even at stock boost levels. Driving one of these cars with no turbo-lag would be exhilarating to say the least.

i wanna hear what MR "ill buy one" has to say

Just a question. In your part drawing you show the bearings located in the compressor housing. It appears there would be a moment created from the exhaust gasses hitting the turbine blades which may cause your shaft to deflect. Does your bearing positioning sufficiently counteract the moment?

Speedy:)

The bearing assembly itself is not what is carrying the load which you are describing, but in fact the wheels themselves are. First of all the wheels are extremely well balanced. While the turbine wheel is being pushed one direction, the compressor wheel inherently wants to be pushed the opposite direction by the air it's trying to compress. This effectively balances the wheels together. Secondly the exhaust gases entering the turbine are not flowing directly at one position of the turbine wheel, but are flowing through the vanes first. By the time the exhaust gases get past the vanes, the gases have been distributed to 15 different areas of the turbine wheel. This not only aids in quick spool-ups, but eliminates the possibility of deflection.

I hope this answers your question.

What about compressor surge?

So, your turbine housings have stator vanes built into them? Do you have any data on backpressure vs boost?

Are there any options for different turbine housing flanges? Would a custom turbine housing with KKK based inlet &outlet flanges allow one of these turbos to potentially bolt up?

Interesting product love to hear more about it.

Taken from our site:

"Understanding Surge Line
The Aerocharger has a very soft surge, which means that turbo flutter is mild and it is capable of quickly recovering. However it is still best to understand what surge is and how it affects power delivery.

Surge is most commonly experienced when one of two situations exist. The first and most damaging is surge underload. This can be an indication that your compressor is too large for your application. Surge is also commonly experienced when the throttle is quickly closed after boosting. This occurs because mass flow is drastically reduced as the throttle is closed, but the turbo is still spinning and generating boost. This immediately drives the operating point to the far left of the compressor map, right into the surge line. The surge line is left hand boundary of the compressor maps below. Operating to the left of this line represents a region of flow instability. On a conventional turbocharger this region is characterized by mild flutter to wildly fluctuating boost and “barking” from the compressor.

Surge will dissipate once the turbo speed finally slows enough to reduce the boost and move the operating point back into the stable region. Aerocharger surge is hardly noticeable, where as conventional turbo surge is hard. A hard surge is very noticeable along with a sudden flutter of power. This is less than desirable and potentially disastrous. One example would be on a motorcycle when trying to roll into the throttle for a fast exit out of a hard turn."

Most importantly surge is very avoidable as it is typically a characteristic of an improperly sized turbo. A properly sized turbo for your application should be avoiding the surge line. However in some scenarios a proper BOV/BPV (like the three-chamber Synapse valves) can control compressor surge on deceleration very well.


There is a video on our site showing the positive delta condition when datalogging our turbos. Positive delta is a condition where the turbo produces more boost than backpressure.

Aerocharger Positive Delta


This was our hope when we were initially building our 930 kit as well do to the fact that our turbo utilizes the same turbine inlet flange as the factory turbo. But unfortunately since there is no bearing assembly in between the two housings the compressor outlet sits back towards the turbine housing. Even if we supplied turbos with various flange options the dimensions of the turbos are different than that of a conventional turbo. Though you may be possible to take up the slack on a 951, it did not work on the 930 as the location of the compressor outlet needs to line up perfectly with the tins. It ended up working out for the best on our project 930 however. I now have the turbo center mounted like the 934 race cars with a header design far superior to that of the side mounted turbo headers.

^^^^^so no version available, or likely to be available for the 951?

We have a turbo that matches the engine very well, but as stated in my last post it would more than likely not be a direct bolt-on. This is simply because our turbos are slightly different dimensions than other turbos due to the location of our bearing assembly compared to conventional turbos. However for those with aftermarket intercoolers, air intakes, etc. it would be much easier as the plumbing could easily be adjusted to fit. An example would be something like this:

http://www.aswest.net/images/951-07-engine-rf.jpg
^This would be a very simple intercooler and air intake setup to adapt to an Aerocharger. Depending on the diameter of the piping/silicone couplers it may even bolt right up. I have a lot of experience with 911's but none with 951's so if somebody could get me some rough dimensions on the turbo flanges it uses I could determine if any of the exhaust would need to have our flanges welded on or if stock could be used.

To elaborate further on why our turbo will not fit in the factory location on the 930 here is a diagram showing the difference in the distance between the compressor outlet and turbine outlet.

http://img.photobucket.com/albums/v6...Comparison.jpg

It's not much but it was enough to cause the compressor outlet to not line up with the factory hole in the tins on the 930. This is why we opted to go with a 934 based design and mount the turbo in the center. This ended up working out for the best as we were able to change the header to a much greater design, far better suited for fast spool-ups.

This may also be the case with the 951. I look at it as a good thing if you have to alter the header a bit. It would give the opportunity for improvement as the factory 951 header is not the most efficient for fast spool-ups.

So how do you control the vanes? Do you need a seperate or new computer or are they controlled mechanically?

The vanes are operated mechanically via the "controller", which is very similar to the waste-gate actuator on internal wasategate turbos. The controller consists of a diaphragm, piston, spring, and shims. The controller pulls vacuum/boost signal from the charge side of the turbo system (preferably near the compressor outlet) and responds accordingly, adjusting the angle of the vanes to create peak efficiency of the turbine.

http://img.photobucket.com/albums/v6...controller.jpg

The air fitting on the controller is what controls when the vanes begin to activate. A jam nut hold this fitting in place and allows for some adjustment. the spring withing the controller is your main boost adjustment. Swapping out different springs nets different boost ranges which are fined tuned via a series of shims. However if your are comfortable where your boost is and would like to use a manual boost controller, it could simply be installed in-line to the air fitting to act as a bleed-off. This will show the turbo less boost than it's making, in turn building more boost.

Personally I'm a fan of setting the boost where I want it and leaving there unless I have a way to adjust fuel maps on the fly as well, but some people like to have adjustment

it sounds like this would be perfect for a stand alone EMS system to control, compensating for different engine loads/rpm's.

from the diagrams, it doesn't look like it will fit on a 951 because the factory turbo mounts at the center section to the motor support bracket.

at the very least, the stock motor bracket would have to be heavily modified or most likely replaced with a custom bracket to fit this turbo.

fyi, here's a photo of the underside of the turbo on a 951 (looking up from underneath), you can see the tight clearance where the center section mounts to the factory motor bracket;
http://gallery.silentmedia.com/d/61588-1/IMG_2312-2.jpg

Though my experience with 951's may be limited I have seen some of these cars with the turbos mounted in different locations than stock. With that they must be using a machined adapter block of some sort. From the looks of it making a part to bypass the stock turbo and mounting an Aerocharger slightly forward of the stock turbo location wouldn't be out of the question at all.

Which of your turbos would you recommend for the 951?